1. Field of the Invention
The invention relates to an apparatus for blow-molding hollow articles, in particular bottles, made of thermoplastic material. The apparatus comprises a rotatably driven rotary heating member, a plurality of parison carrying mandrels, means to hold and transport said mandrels at the periphery of the rotary heating member, an input station for feeding parisons, heating means to heat the parisons to a blowable temperature, a rotatably driven rotary blowing member including a plurality of blow molds, a transfer station between the rotary heating member and the rotary blowing member and an output means to remove the finished articles, wherein the longitudinal axis of said parisons extend parallel with respect to the rotary axis of both rotary members.
2. Description of the Prior Art
A machine of this type in which all individual rotary members are continuously driven has been suggested in German Patent No. 1 704 119. According to this proposal a first rotatable table is disclosed carrying means to make parisons having a closed bottom portion and a finish at the opening for later receiving a closure. On the table, tube-like portions are gripped intermediate their ends which are heated to welding temperature. For closing the bottom and shaping the finish the tube is then held at a blowing mandrel, having a forward end defining a die core to close the bottom and further including a movable annular die member to shape the finish of the bottle. The blowing mandrel carrying the ready parison is then transferred to the heating table where it is heated along its length to a blowing temperature and is subsequently blown into the hollow article while being carried on a blowing table where the lower ends of the blowing mandrels are connected to a blowing medium pressure source.
Thus the blowing mandrel of this machine allows for performing a number of steps such as to supply blowing medium to the parison and further to shape the parison in closing the bottom portion and forming the opening. This results in a relatively complex structure which weighs the more as all the parisons circulating in the apparatus have to be carried by the blowing mandrels. Accordingly, this necessitates a very large number of blowing mandrels. Further the known type of mandrel does not allow to center and to expand the parison during the blow mold step. In particular, expanding the parison is a desirable feature to gain a biaxial orientation of the plastic material by axially expanding the parison during blowing to obtain an increased rigidity of the finished article.
After blowing the article in the known machine the blow mold is opened and the bottom of the article engaged by a vacuum bell to draw off the article from the blowing mandrel. This operation takes place at the blowing table so that subsequently the blowing mandrels are returned directly onto the first table which is the parison shaping table, while the articles are carried to an output conveyor. However, in case where an article is burst or cracked the vacuum bell cannot attract the article bottom so that the blowing mandrel including the waste has to be removed. This is the reason for providing an additional feeding station for blowing mandrels at the parison shaping table to replace blowing mandrels which had to be disposed. This renders the structure still more complex.
German Patent No. 2 141 249 discloses a further embodiment of a blowing mandrel allowing to centering and expanding the parison during the blow mold step. The end of the blowing mandrel extending into the parison carries a piston-like sleeve which is displaced by the blowing pressure to axially guide and expand the parison. The blowing medium enters the parison through a throttling section between the mandrel end and the sleeve. This type of mandrel is expensive to manufacture.
Nevertheless the known machine offers many advantages to blow mold great numbers of articles, in particular due to a continuous operation. For example this would be not possible in a machine operating step by step.